1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing beads for artificial pearls used for various personal ornaments (e.g., necklaces, rings, bracelets).
2. Description of the Related Art
Such artificial pearls are produced from beads formed of a synthetic resin that is relatively inexpensive and capable of being mass-produced, which are used for various personal ornaments by applying a pearl solution having a color similar to a natural pearl to beads in every shape and form.
As primary materials of the artificial pearls, various kinds of synthetic resins may be used. Among them, a urea resin is most used.
The urea resin by nature has easy formability and relatively easy polishing process as the bead in view of hardness, weight, thermosetting capability, etc., thus being very widely used as the artificial pearl bead.
For a conventional method and apparatus for manufacturing artificial pearl beads, in the case of beads taking a circular shape when being seen in cross section (alternatively, an oval, semi-circular, triangular or quadrilateral shape), upper and lower moulds having semi-circular grooves are heated at a preset temperature. A powdered urea resin is poured into the semi-circular grooves of the lower mould, and then the upper mould is lowered to come into close contact with the lower mould. Subsequently, the urea resin is cured in the semi-circular grooves by heat from the upper and lower moulds, so that the circular beads are molded. In the case of perforated beads with a through-hole, a drilling pin for making the through-hole is provided in the center of each of the semi-circular grooves of the upper or lower mould. Thus, the beads are drilled while being molded. In the case of solid beads without a through-hole, the upper and lower moulds are provided only with the semi-circular grooves.
This conventional method and apparatus for manufacturing artificial pearl beads makes use of pressure, which has many problems.
These problems are as follows:
1) The beads are molded by pouring the urea resin into the semi-circular grooves of the fixed lower mould, and then by lowering the movable upper mould. Hence, an air pressure generated from the upper mould moving down at a constant speed has influence on the powered urea resin, so that the powered urea resin are scattered. In order to prevent this phenomenon, when the upper mould moves down at a slow speed, productivity drops remarkably.
2) The beads are produced only by primary moulding, so that there is a high possibility of air or gas generating bubbles in the bead. Furthermore, even a surface of the bead is provided with such bubbles or cracks. Accordingly, the bead undergoes deterioration in the value of commodities.
3) It is the most important problem that harmful gases generated when the urea resin are cured by hot heat are not properly discharged, thus being responsible for generation of the bubbles. Thereby, even the finished bead contains such harmful gases.
When artificial pearls finished from the beads containing these harmful gases are used as personal ornaments, the harmful gases leak out throughout a long period. As a result, various skin diseases such as a rash and an itching are generated.
For this reason, advanced nations impose intense restrictions on a permissible content of the harmful gases which the synthetic resin bead for the artificial pearl contains.
4) In the case of the beads with a through-hole, it is difficult to manufacture the mould because the drilling pin is formed in the semi-circular groove in which the bead is molded. In addition, it is very hard to separate the molded beads from the mould.